Is Gladehart Cavalry legal in Standard, Modern, and Commander?

Gladehart Cavalry is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

Gladehart Cavalry

Q: What type of card is Gladehart Cavalry?

Gladehart Cavalry is a Creature — Elf Knight. Its oracle text reads: "When this creature enters, support 6. (Put a +1/+1 counter on each of up to six other target creatures.) Whenever a creature you control with a +1/+1 counter on it dies, you gain 2 life. Power/Toughness: 6/6"